'If you don't go after the network, you're never going to stop these guys. Never.'

BAGHDAD -- In the early spring of 2006, perhaps the most important document in Baghdad was known as the MOASS -- the Mother of All Spreadsheets-- a vast compilation of radio frequencies that insurgents used to trigger roadside bombs.

In some areas of Iraq, 70 percent of all improvised explosive devices were radio-controlled, and they caused more than half of all American combat deaths. An overworked Army intelligence officer tracked the frequencies, and an equally overworked Navy electrical engineer matched them against 14 varieties of electronic jammer used by coalition forces.

As new frequencies popped up, the updated MOASS was analyzed by the National Security Agency, by Navy electronic warfare specialists in Maryland and by Army specialists in New Jersey, which led to recommended adjustments in the jammer settings. Those modified "loadsets" were then e-mailed to U.S. military forces throughout Iraq so that the jammers could be reprogrammed. The cumbersome process took weeks, by which time new frequencies had been logged into the spreadsheet, requiring further analysis and further reprogramming even as hundreds of new jammers arrived in Iraq each month. "It was a mess," a senior defense official recalled.

By the end of 2006, the Department of Defense had spent more than $1 billion during the year just on jammers. Fielding them "proved the largest technological challenge for DOD in the war, on a scale last experienced in World War II," according to Col. William G. Adamson, a former staff officer for the Joint IED Defeat Organization (JIEDDO), the Pentagon office coordinating the campaign.

The U.S. strategy was defined in six words: "Put them back on the wire." By neutralizing radio-controlled bombs, the jammers would force insurgent bombmakers to use more rudimentary triggers, such as command wire. Those triggers would be simpler to detect, in theory, and would bring the triggermen closer to their bombs, where U.S. troops could capture or kill them.

That strategy has succeeded. In the subsequent 18 months, radio-controlled bombs would shrink to 10 percent of all IEDs in Iraq. Today, bombs triggered by simple command wire have increased to 40 percent of the total.

But the threat from IEDs has barely diminished. In the first seven months of this year, there were 20,781 roadside bomb attacks in Iraq, one every 15 minutes. And as of this morning, IEDs have killed 440 U.S. troops this year. Putting them back on the wire has proved a mixed blessing.

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Different jammers worked by different means. Active jammers screamed constantly, disrupting radio-controlled bombs with a barrage of radio waves on pre-selected frequencies that drowned out the triggering signal. Reactive jammers "scanned and jammed" by monitoring the electromagnetic spectrum -- like a human ear in a crowded restaurant listening for a voice that whispered "detonate, detonate, detonate" -- and then blocked the frequencies they were programmed to block.

Since the invasion of Iraq in March 2003, a hodgepodge of jammers had arrived in Mesopotamia, both active and reactive, weak and powerful: Warlock Green, Warlock Red, Warlock Blue, ICE, MICE, SSVJ, MMBJ, Cottonwood, Jukebox, Symphony. Collectively they were now known as CREW, an awkward acronym within an acronym: counter radio-controlled IED electronic warfare.

As more jammers flooded the war zone, the mess grew messier. For many months, the shortcomings in electronic warfare expertise had been evident among Army and Marine units. "We had all these boxes over there and people didn't know how to use them," said Rear Adm. Arch Macy, commander of the Naval Surface Warfare Center. "They'd turn them on, thinking they were protected when they weren't."

Electronic "fratricide" intensified, with more instances of jammers disrupting coalition radios and even the radio links to unmanned aerial vehicles. More troops switched off their CREW systems rather than risk disrupting their radios; rumors circulated that jammers actually detonated IEDs.